The present invention relates to a surgical fastener or device (implant) formed in the shape of an arrow comprising a shaft with a proximal (first) portion having protrusions and a blunt end and a distal (second) portion having protrusions and a pointed end, the protrusions of the proximal and distal portions configured to lock the implant in a position inside a soft and/or tough tissue according to the use of the implant. The implant may be manufactured of a polymer or a polymeric compound which is substantially (bio)absorbable in tissue conditions and contains oriented reinforcing structure or the like of a polymer or polymeric compound or ceramic bioglass compound.
The surgical implant of the invention is particularly but not solely intended to be used in repair surgery of traumas of soft and/or tough tissues containing fibrous structures, such as knee meniscal tissues.
With reference to the prior art in the field it has been shown that fixation of meniscus traumas like ruptures and lesions by suturing with absorbable sutures gives better results than removal of traumatized meniscal tissue, see e.g. N. A. Palmeri, T. F. Winters, A. E. Joiner and T. Evans, xe2x80x9cThe Development and Testing of the Arthroscopic Meniscal Staplexe2x80x9d, Arthroscopy, Vol. 5, No. 2, 1989, p. 156 (Ref. 1). However, arthroscopic suturing is a complicated and tedious technique where risks for the patient are significant because of danger to vessels and nerves. Additionally, the suturing of meniscus ruptures leaves a single or several loops of sutures, which can irritate joint cavity tissues. Therefore, for a long time surgeons have desired an absorbable meniscus lesion fixation device, like a staple or fastener, which has the advantages of absorbable suturing techniques but which can be used more rapidly and safely than sutures.
Several research groups have tried to develop absorbable meniscus lesion fixation devices such as clamps. However, the various demands upon such a device are high. It must be strong enough to maintain good contact of lesion tissues after the operation so that rapid healing occurs. The device must retain its strength long enough for good healing. It must be absorbed without causing complications that would prevent the healing of the lesion. Additionally, the installation of the device should be easy and rapid and should cause minimum operational trauma. Because of these high demands, an optimal absorbable meniscus lesion fixation device has not been developed yet. Palmeri et al. reported in Ref. 1 the development of a method of meniscal repair using arthroscopically applied absorbable fasteners. However, the reported method was complicated because the final design used cannulation of the staple for needle-guided placement. Additionally, staple fracture, migration and articular abrasion was found.
With regard to implants known in this field, reference is made to U.S. Pat. No. 4,873,976 which discloses an arrow-like implant particularly intended for the surgical repair of meniscal ruptures. However, the arrow-like implant according to this publication has the disadvantage that particularly its proximal end (stem) is shaped as a plate in a way that the direction of the main plane of the plate is perpendicular to the longitudinal direction of the arrow""s body. Because of this fact, it is particularly difficult to install the implant, because the channel used to install the implant must have the cross-sectional shape of the stem; it is difficult to guide the implant in the installation channel, because the guiding effect is substantially brought upon the stem only, and not the body of the arrow. Furthermore, the structure of the stem causes tissue irritation and abrasion, particularly when placed in connection with the meniscus because the stem is usually left protruding to a high degree from the outer surface of the meniscus.
Bays et al. (U.S. Pat. Nos. 4,884,572 and 4,895,141) describe a surgical-repair tack and applicator and method of using them. The tack has a barb member, a shaft portion and a grip portion. The tack is made of biodegradable material having a degradation time selected to coincide with the healing time of the tissue. In an alternate embodiment, the tack""s barb comprises a continuous helical barb. A disadvantage of this tack is that the grip portion is bulky and may remain on meniscal surface causing irritation inside a joint cavity.
The method and apparatus for repairing a meniscal tear disclosed by Winters (U.S. Pat. No. 5,059,206) comprises a fastener having protrusions or barbs that is applied to a meniscal tear with a delivery device. The delivery device has a flexible tip that is manipulable through a curved radius to enable the surgeon to insert the device into the central part of the knee and then extend the fastener radially outward into and across a meniscal tear. Also in this case the proximal end of the fastener is bulky and protrudes partially above and/or below the outer surface of the meniscus.
Tamminmaki et al. (U.S. Pat. No. 5,562,704) disclose an arrow-like bioabsorbable implant particularly intended for the surgical repair of meniscal ruptures. This implant does not have the guiding or abrasion problems that implants of U.S. Pat. No. 4,873,976 or U.S. Pat. No. 5,059,206 may have. However, a disadvantage of U.S. Pat. No. 5,562,704 is that the proximal part of the implant (the wings) preferably remains on the surface of the meniscus, so that when the wings break as a consequence of bioabsorption, the broken wings may irritate knee joint tissues. If the proximal part with the wings is desired to be located inside of meniscal tissue, the surface capsule of the meniscus must be cut horizontally with a special cutting blade. This lengthens the operation time and causes substantial damage to the meniscus surface.
U.S. Pat. No. 5,569,252 describes a fastener, an installation device, and method for repairing tears in the soft tissue of a patient, including meniscal tears. The fastener has a variable-pitch helical protrusion along a central portion that decreases from the distal end to the proximal end, which can serve to bring two sides of the tear into apposition as the fastener is advanced across the two sides of the tear in a screwing motion. This implant, which needs a screwing motion for installation, is slow and tedious to use arthroscopically and the turning of the implant through fibrous tissue, such as meniscus tissue, has the risk that the fibrous tissue may twist around the turning implant, hindering or preventing the installation of the implant.
Orthopedic and Musculoskeletal Markets Biotechnology and Tissue Engineering, Medical Data International, Inc., Irvine, Calif., USA, February 1997, p. 1-17 describes a bioabsorbable device for meniscal repair. This device has two legs with molded barbs that are attached by a flexible member composed of resorbable suture. The device is installed into a meniscus with an arthroscopical tool so that the legs penetrate the rupture of meniscus to hold the edges together. The disadvantage of this device is that the suture loop remains on the surface of meniscus where it can cause irritation. Additionally, the two-leg device requires a bulky installation tool which makes arthroscopical installation of the device difficult.
It is an object of the present invention to provide a bioabsorbable fastener that allows a minimally invasive method for repairing a tear in soft or tough tissue.
It is a further object to provide such a fastener that is rapid and easy to install and gives a strong and safe fixation of the tissue tear and that may be made from a nontoxic, biocompatible bioabsorbable polymer, polymer alloy or fiber reinforced polymer composite, specially designed to maintain its structural integrity during the healing of the tear and to prevent tissue abrasion.
It is an additional object to provide such a fastener having a shape designed to compress the tear.
It is a further object to provide a device (fastener) which will be shot totally inside of soft or tough tissue, like meniscal tissue, to penetrate the tissue (meniscal) tear and to hold the ruptured edges together.
These and other objects are attained with the fastener of the present invention.
The fastener of the present invention is designed for repairing a tear in soft and/or tough tissue of a patient, such as a tear of the meniscus within the knee.
The implant has a shaft with a proximal (first) portion formed with protrusions in relation to the surface of the shaft and having a blunt end and a distal (second) portion formed with protrusions in relation to the surface of the shaft and having a pointed end. The purpose of the protrusions is to arrest (lock) the implant inside of the soft and/or tough tissue after installation.
Accordingly protrusions emerge from both the proximal and distal portions of the device. The protrusions are typically barbs, scales, threads, serrations, ridges or the like. The protrusions at the distal portion of the shaft of the device prevent the installed device from slipping out of the meniscal tissue in the direction opposite to the direction of installation and the protrusions at the proximal portion of the shaft prevent the installed device from further penetrating the meniscal tissue in the direction of installation. This behavior is achieved with the special geometry of the protrusions.
In a preferred embodiment the protrusions of the distal portion of the shaft of the device are formed so that they facilitate the slipping of the device into the meniscus during insertion but they resist the slipping of the device in the direction opposite to the installation direction. On the other hand, the protrusions of the proximal portion of the shaft of the device are formed so that they stop the device inside of meniscal tissue when the device has been shot into the meniscus with the delivery (installation) tool. Both sets of protrusions, acting together, exert an advantageous compression to the ruptured surface when the device is shot into the meniscus and across the rupture. This compression serves to close the rupture and promotes healing.
A further advantageous feature of the device is that the surface of the shaft may include longitudinal ridges.
Protrusions that are manufactured on these ridges are more effective at preventing unwanted movement of the installed fastener and maintaining compression of the rupture. Because of their increased prominence, it is also easier to manufacture protrusions on ridges. Moreover, the ridges unexpectedly promote healing of the rupture by providing channels along the interiors of the ridges through which beneficial blood flow can occur along the length of the device. These channels, which are about 0.05-0.5 mm wide, act as capillaries, transporting blood from the highly vascularized distal portion of the meniscus to the poorly vascularized proximal portion of the meniscus. Further, the ridges help to guide the fastener through the cannula of the installation instrument and into the meniscal or other soft tissue during installation.